Thank you for the answer!
I have a 'La Rambla' aswell and although these two do share some similarities I'm not sure the "mystery coleus" is 'La Rambla'.
I have quite an extensive indoors all year round coleus collection and I try my best to find out the names for each one, which can be difficult seeing how I haven't bought any from a nursery so there are no name-tags to look at ;)
This is one of the few varieties that have me stumped! (and it is kinda p**sing me off to be honest!
)